You're already starting with a full list of contacts from your smartphone address book. +Guys have prepared also some tweaks for distribution.

But, none of my other contacts will have a status unless they have your app, right?

But you can invite them to use it, it's the simplest and fastest way

I see, but what if I only have a mobile number available for some of my contacts. Will it send them a text asking them to join?

I'm sure it's going to be an awesome app though, I'll happily sign up. I'd like an easier way to take my friends with me. Also, I'd love Twitter integration.